Numbers of workers have studied the influence of magnetization on the dynamics of gasfluidized solids in batch beds. An early account of this phenomena was reported by M. V. Filippov [Applied Magnetohydrodynamics, Trudy Instituta Fizika Akad. Nauk., Latviiskoi SSR 12:215-236 (1960); Zhurnal Tekhnicheskoy Fiziki, 30 (9):1081-1084 (1960); Izvestiya Akad. Nauk., Latviiskoi SSR, 12(173): 47-51 (1961); Izvestiya Akad. Nauk.:Latviiskoi SSR, 12:52-54(1961); and Aspects of Magnetohydrodynamics and Plazma Dynamics, Riga (1962), Izvestiya Akad. Nauk., Latviiskoi SSR, pp. 637 to 645]. Subsequent workers have reported on the influence that magnetization exerts on pulsations, heat transfer, structure, and other characteristics of magnetized and fluidized solids in batch beds. A review of some of this work is given by Bologa and Syutkin [Electron Obrab Mater, 1:37-42 (1977)]. Ivanov and coworkers have described some benefits of using an applied magnetic field of fluidized ferromagnetic solids in the ammonia synthesis process and some of the characterizations for this process [see British Pat. No. 1,148,513 and numerous publications by the same authors, e.g., Ivanov et al, Kinet. Kavel, 11(5):1214-1219(1970); Ivanov et al, Zhurnal Prikladnoi Khimii, 43, 2200-2204 (1970); Ivanov et al, Zhurnal Prikladnoi Khimii, 45:248-252 (1972); Ivanov et al, Chemical Industry, 11; 856-858 (1974); Shunkov et al, Zhurnal Prikladnoi Khimii, 49 (11):2406-2409 (1976)]. Various means for operating magnetic fields to stabilize the bed of fluidized magnetizable solids have been disclosed in U.S. Pat. Nos. 3,440,731; 3,439,899; 4,132,005 and 4,143,469 and Belgium Pat. No. 865,860 (published Oct. 11, 1978).
R. E. Rosensweig [Science, 204:57-60 (1979), Ind. Eng. Chem. Fundam., 18 (3):260-269 (1979) and U.S. Pat. Nos. 4,115,927 (now reissued as U.S. Pat. No. Re. 31,439 on Nov. 15, 1983) and 4,136,016 (now reissued as U.S. Pat. No. Re. 31,186, on Mar. 22, 1983)] reported on a number of features of magnetically stabilized fluidized magnetizable solids and a systemmatic interpretation of the phenomena. In these publications and patents, R. E. Rosensweig reported on the quiescent fluid-like state for the magnetically stabilized fluidized bed (MSB), particularly one which is totally free of bubbles or pulsations when a uniform magnetic field is applied to a bed of magnetizable solids, approximately colinear with the direction of the fluidizing gas flow. As such, this magnetic stabilization produces an unbubbling fluid state having a wide range of operating velocities. These velocities are denoted as a superficial fluid velocity ranging between (a) a lower limit given by the normal minimum fluidization-superficial fluid velocity required to fluidize the bed of solids in the absence of an applied magnetic field, and (b) an upper limit given by the superficial fluid velocity required to cause time-varying fluctuations of pressure difference through the stabilized fluidized bed portion during continuous fluidization in the presence of the applied magnetic field. It is disclosed in Rosensweig's U.S. Pat. No. 4,115,927 that the stably fluidized solids resemble a liquid and as such enjoy the benefits that the solids are facilitated for transport while, concomitantly, the pressure drop is limited to that of a fluidized bed. In addition, the beds exhibit the absence of the backmixing normally associated with fixed bed processes. At column 6, lines 63-66, of the '927 patent, it is stated: "The fluidized bed thus formed has many properties of a liquid; objects float on the surface and the addition or withdrawal of solid particles in process equipment is also facilitated." The '927 patent further states that "orifice discharge tests confirm the ability to transfer solids out of the containing vessel" (column 8, lines 58-59 ). Further, in column 21, lines 17-24, it is stated: "The utility of the magnetically stabilized compositions in applications such as absorptive or adsorptive separation of vapor species, catalyst utilization and regeneration, particulate filtration, subsequent bed cleaning, reaction of solids in moving beds and allied applications in which bed solids must be transported to and from the bed depend on fluidized solids depending as a medium capable of flowing in response to a pressure differential."
Although Rosensweig discloses the possibility of transporting solids in an magnetically stabilized bed from vessel to vessel, all of the reported experiments involved batch beds.
Others have reported the use of continuously flowing cocurrent or countercurrent magnetically stabilized fluidized beds with a variety of chemical reactions in adsorptive or absorptive processes. U.S. Pat. No. 4,247,987 to Coulaloglou et al, issued Feb. 3, 1981, relates to a process for continuous countercurrent contacting to absorb one species from a contacting fluid by use of at least one magnetically stabilized fluidized bed. Similarly, U.S. Pat. No. 4,292,171, issued Sept. 29, 1981 and U.S. Pat. No. 4,294,688 to Mayer, issued Oct. 13, 1981, disclose catalytic hydrocarbon conversion processes in which magnetizable particles with or without separate catalytic particles are passed countercurrent to the hydrocarbon feed to effect a chemical conversion. U.S. Pat. No. 4,319,892 to Waghorne et al, issued Mar. 16, 1982 and U.S. Pat. No. 4,319,893 to Hatch et al, issued Mar. 16, 1982, teach an adsorption process for the separation of hydrogen from a feed gas or vapor which contains hydrogen in admixture of one or more hydrocarbon components. Each process uses a set of vertically stacked magnetically stabilized fluidized beds to effectuate one or more steps in the adsorption-desorption process. The adsorbent passes through each of the MSBs in a direction countercurrent to its particular gas flow.
However, none of the noted patents suggest the use of fluid redistribution buffer trays in which the fluid flows in a solids-free zone as the solids pass in a separate channel between magnetically stabilized fluidized beds.
It has now been found that although magnetically stabilized fluidized beds offer many advantages as a solid-fluid contactors for chemical processes and separations, in some operations low radial dispersion properties associated with MSB media, as in packed particulate media, can be a deterrent to good fluid mixing or distribution. This is especially true in those instances where uniform feed introduction or product withdrawal is desired; that is to say, that the lack of radial dispersion in a magnetically stabilized fluidized bed may, in some instances, result in residence times which vary to some moderate extent across the diameter of the bed. This problem can be solved in a number of different ways but most of them involve deletion of one or more of the unique benefits attributable to MSBs.
Others teach methods of decoupling solids from fluid flow in fluidized beds. None, however, suggest the buffer means disclosed herein, nor do they suggest such a decoupling in concert with a magnetically stabilized fluidized bed. For instance, U.S. Pat. No. 3,309,305 to Scott, issued Mar. 14, 1967, discloses a vessel containing fluidized beds which are separted by "velocity modifying means". The modifying means are generally some variation of end-to-end truncated cones designated to generally separate passage of solids downwardly from passage of liquid or gas one way or the other. As depicted in Scott's FIGS. 11 and 12, a quench gas may be introduced into the liquid phase through nozzles placed within the velocity modifying means.
Similarly, U.S. Pat. No. 2,429,721 to Jahnig, issued Oct. 28, 1947, suggests the use of a sequence of fluidized beds. Solids flow downwardly through a sequence of vertically oriented beds and the fluidizing gases are removed from the upper end of each bed apparently for subsequent disposal. Additionally, fluidizing gases sent to each bed are said to contain recycled solids.
U.S. Pat. No. 2,639,973 to Fritz, issued May 26, 1953, discloses a column (similar in operation to a bubble-cap distillation tower) containing a series of plates on each of which a fluidized bed is formed. Solids enter the system through an upper inlet and flow to each of the lower fluidized beds through downcomers while the gases flow upwardly through the bubble cap perforated distributor plates.
U.S. Pat. No. 2,883,332 to Wickham, issued Apr. 23, 1959, discloses a vessel containing an upper fluidized bed and a lower fluidized bed with solids from the upper bed flowing through a downcomer to the lower bed. The embodiment shown in Wickham's FIG. 2discloses that the gases from the lower bed flow through an annular sleeve and bypass the second reaction zone.
Another design for use with fluidized beds was repoted by Jobes, as shown in D. Kunni and O. Levenspiel, Fluidization Engineering, Wiley (1969) pp. 29-30. It discloses a two-stage fluidized salt dryer in which a fluidizing gas is withdrawn from the free space above a lower bed, heated, and introduced into an upper bed as the drying medium.
Fluid distributing means for use in or between packed beds are also shown in the literature. U.S. Pat. No. 3,208,833 to Carson, issued Sept. 28, 1965, shows a device for placement in a fixed bed comprising a number of fluid-carrying rings and radials which introduce or remove fluid through axially oriented porous or multi-holed injectors. U.S. Pat. No. 3,214,247 to Broughton, issued Oct. 26, 1965, suggests a chamber between beds with a diametric injector placed in the plane of an interbed baffle. U.S. Pat. No. 3,523,762, also to Broughton, issued Aug. 11, 1970, shows a number of devices for baffling liquid flow between beds. European Patent Application No. 0,074,815, to Haase, published Mar. 27, 1983, shows a complicated arrangement of screens, baffles, and distributors intended to collect the liquid flowing between beds, add or withdraw a liquid at the collection area, and introduce the resulting liquid into a subsequent bed.
As mentioned above, none of these devices disclose an apparatus in which the solids flow through a magnetically stabilized fluidized bed is completely separated from the fluid flow for subsequent distribution into the MSB.